gas guage dilema!

[wildwln]

i just joined this Forum today but i have been visiting here many times in the past, i find the expertise on this site remarkable and i hope to add to it at some point. I am a long time chevy/gmc truck owner and have my cherried out 85 swb 4x4 still after buying it bran new...anyway my son has just purchased a 1/2 ton 74 GMC 454 and is allowing me to do all the work on it!

the fuel guage peggs all the way past the Full marker each time...the truck is equipped with a passenger side tank which appears factory and on the drivers side there is a large metal square gas tank which incidently has no ground wire to the frame altho the passenger side does...these tanks are piped to two solinoid valves located between the two....

so todate i have run a new lead wire from each of the sending tanks down the frame and up into the cabin...i have run a new lead wire from one of the solinoid valves down the frame and into the cabin..(the solinoids are jumpered together with a common wire)...inside the cabin is a simple toggle switch to hook up these wires...i placed a power wire from the toggle post into the fuse box on a ign post...i connected each of my new sending unit leads to the toggle switch...i connected the new lead from the solinoids to the toggle switch and here is where i get stumped..

this is a 5 connector toggle switch and i have 1 power, 2 senders and 1 solinoid connected for a total of 4..i would think my final connection should either to be a frame ground or too the guage itself shouldnt it?...but since the instrument cluster is wired with the plastic panel circuitry at the back, there seems to me no means to hard wire the guage itself...incidentally i tried a spare guage from my 85 in the 74 and it pegged all the way past E-opposite of the original guage which pegged past F...i can hear the solinoids click as i toggle the switch back n forth, but the guage no worky...

i really would appreciate any input and advice you mechanical wizards could offer me at this point, i am flustered and dumbfounded and reaching for the dynamite at this point~~

[tucsonjwt]

I probably can't help you, but just for clarified information for everyone, are the dash switch, switching valve, and sending units a stock set up or is it aftermarket? It seems like your electronics are not stock.
I have gone through all the troubleshooting techniques suggested all over the net and have not yet found a method that is foolproof. I have always had to start with replacing or cleaning/reinstalling one component at a time. You can always check to see that you have power at the switch and gauge when it is activated, but since you can hear the solenoid click it sounds like you have power.
Most people have found that checking/cleaning the ground wire(s) on the frame is the best place to start.
I would disconnect the odd aftermarket tank and see if you can get the stock tank to register correctly, then focus on the other tank.
If you can't get this setup to work, then I would go for replacement stock components. You can check LMC or Classic parts for a price list.

[wildwln]

hey thanks for replying, and to answer your question NO it appears nothing on the truck is stock and from what i can tell most of the work on the truck was probably done by a blind sixth grader after school...thus i have had to replace all the tail light wiring harness, as well as the front harness...and for all the trailer lights as well as the gas tank wiring the PO used all yellow wiring- FOR EVERYTHING!...

what i think i will do is bypass the tank selector toggle switch and concentrate on just getting one tank working with a working gas guage, so if anyone could tell me how the stock wiring went i would be very appreciative...i will eliminate for myself a few headaches that way i think...

anyone know how a single tank is wired from the factory on a 74??

[motornut]

Welcome
if your going past full
check the sending unit wire
if it is off it goes high
grounded goes empty

[sixshooter798]

http://67-72chevytrucks.com/vboard/s...45#post4237845

[wildwln]

well after an eventful investigation at the local PicnPull, i found an exact replica of my sons truck with all the wiring and pieces i needed to see for a proper hookup!!

it was mainly that notorious brown/tan wire that was at fault

thanks for all the help,

[nelsonadam84]

First I would see what your ohms are for you gauge. I would check your ground wires. Your best tool for this job is a multimeter and a wiring diagram. Wish I could tell you more but I don't have my books with me.